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The effect of ash composition on gasification of poultry wastes in a fluidized bed reactor Fabrizio Di Gregorio, Donato Santoro and Umberto Arena Waste Manag Res 2014 32: 323 originally published online 17 March 2014 DOI: 10.1177/0734242X14525821 The online version of this article can be found at: http://wmr.sagepub.com/content/32/4/323
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WMR0010.1177/0734242X14525821Waste Management & ResearchDi Gregorio et al.
Original Article
The effect of ash composition on gasification of poultry wastes in a fluidized bed reactor
Waste Management & Research 2014, Vol. 32(4) 323–330 © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0734242X14525821 wmr.sagepub.com
Fabrizio Di Gregorio1, Donato Santoro2 and Umberto Arena2
Abstract The effect of ash composition on the fluidized bed gasification behaviour of poultry wastes was investigated by operating a prepilot scale reactor with two batches of manure obtained from an industrial chicken farm. The experimental runs were carried out by keeping the fluidized bed velocity fixed (at 0.4m s−1) and by varying the equivalence ratio between 0.27 and 0.40, so obtaining bed temperature values between 700 and 800 °C. The performance of the gasification process was assessed by means of mass balances as well as material and feedstock energy analyses, and reported in terms of cold gas efficiency (CGE), specific energy production, low heating value of obtained syngas and yield of undesired by-products. The experimental results indicate the crucial role of ash amount and composition of the two poultry wastes. In particular, higher ash content (25.1% instead of 17.2%) and higher fractions of calcium, phosphorous and potassium (with an increase of 24, 30 and 28%, respectively) induce a dramatic reduction of all the process performance parameters: CGE reduces from 0.63 to 0.33 and the specific energy from 2.1 to 1.1 kWh kgfuel−1. At the same time, the formation of alkali compounds and their behaviour inside the fluidized bed reactor determine an increase of feedstock energy losses, which is related to occurrence of sintering and bridging between bed particles. Keywords Chicken manure, poultry waste, gasification, bubbling fluidized bed, sintering, feedstock energy: wmr 13-0233
Introduction The intensive increase in the worldwide population implies an exponential growth in the demand for food. This aspect, together with the low production cost of poultry meat has led to a growing number of intensive farms and to a rapid expansion of the global market. For instance, the Italian poultry industry, which is one of the Europe’s largest producer and exporter of poultry meat (covering about 12% of the overall market), generates a turnover of €5300 million, mainly related to the national consumption (UNA, 2010). At the same time, the proliferation of chicken farms produces millions of tons of manure by-products which, until the beginning of 2000, were conventionally sent to landfill. The necessity for an adequate treatment of pathogen agents and heavy metals (Jackson et al., 2006) and for avoiding potential eutrophication effects (Heathman et al., 1995) has led to stringent environmental legislations (Boesch et al., 2001; Dagnall et al., 2000) and to the requirement of alternative management options. The bio-chemical (composting and anaerobic digestion) and thermo-chemical (combustion and gasification) conversion processes, as well as their possible combinations, have been recently assessed as potentially sustainable management solutions (Cantrell et al., 2008). The bio-chemical units allow mass and volume reduction together with the destruction of pathogens but they need
additional equipment and handling costs and appear not suitable to solve the aspects related to nutrient losses and heavy metal contamination (Florin et al., 2009). The thermo-chemical units appear to be more convenient from the economic and environmental points of view, owing to their capability to destroy pathogen agents, to remarkably reduce the mass of waste, and to provide a certain amount of energy (Zhu and Lee, 2005). In particular, gasification may be used to convert the poultry farm waste into a fuel gas (‘syngas’), which can be efficiently burned in a dedicated energy conversion device (Zhang et al., 2009). On the other hand, problems associated with the formation and release of different contaminants (tar, ashes, heavy metals, 1AMRA
s.c. a r.l. – Analysis and Monitoring of Environmental Risk, Via Nuova Agnano, Naples, Italy 2Department of Environmental, Biological and Pharmaceutical Sciences and Technologies – Second University of Naples, Caserta, Italy Corresponding author: Umberto Arena, Department of Environmental, Biological and Pharmaceutical Sciences and Technologies – Second University of Naples, Via A.Vivaldi, 43, Caserta, 81100, Italy. Email: [email protected]
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halogens and alkaline compounds) could cause environmental and operating problems, such as wastewater pollution; material corrosion; clogging or blockage in fuel lines, filters, heat exchangers and energy conversion devices (Arena, 2012). These aspects still represent some crucial obstacles to be overcome. The study aims to evaluate the performances of an air gasification process of chicken manure, carried out in a bubbling fluidized bed reactor operated under different values of equivalence ratio (defined as the oxygen content of air supply with respect to that required for the stoichiometric complete combustion of the fuel effectively fed to the reactor). Fluidization is the most promising among all biomass gasification technologies, due to its peculiar characteristics and, in particular, the possibility of utilizing different fluidizing agents, reactor temperatures and gas residence times, to inject reagents at different reactor heights and to operate with or without a specific catalyst (Arena, 2013; Basu, 2010). An appropriate utilization of these features could thus be the key to an efficient and sustainable management of this kind of waste.
Material and methods Characterization of chicken manure tested Two batches of chicken manure derived by an Italian poultry farm, as collected in two different seasons, were used as feedstock. The wastes, identified in the following as CM1 and CM2, were both obtained by the same random sampling method in the chicken farm storage area. Their ultimate analysis was obtained by means of a Leco Truspec CHNS analyser, while the composition of the inorganic fraction was determined by an Agilent 7500 ICP-MS. Table 1 reports these analyses together with the moisture and ash contents, and the heating values evaluated by means of the relationship proposed by Sheng and Azevedo (2005). It is worth noting that the data in Table 1 are very close to those reported by the main scientific literature in the field (Davalos et al., 2002; Font-Palma, 2012; Giuntoli et al., 2009; Quiroga et al., 2010). Figure 1 shows the thermal analyses of the two wastes, as obtained by a Perkin-Elmer Pyris Diamond thermogravimetric differential thermal analyser (TG/DTA), operated with nitrogen and at a heating rate of 20 °C min−1. The curves of TG (sample weight losses) and DTA (endo- or exo-thermic nature of the reactions) seem to predict a sufficiently similar behaviour of the two wastes, with most of the material decomposed between 280 and 710 °C. This range is quite similar to those found by Giuntoli et al. (2009), who analysed an untreated and a leached chicken manure and by Otero et al. (2011), who analysed a manure characterized by a very similar ultimate analysis. It is likely that the first peaks along the DTA curve (i.e. those around 280 and 320 °C) represent the decomposition of non-digested food, which occurs with the release of ammonia contained in the manure (Font-Palma, 2012). The other peaks are probably due to the decomposition of the manure, with the release of methane at about 530 °C. The last peak (at about 770 °C) could be related to
Table 1. Main chemical properties of the chicken manure utilized for the gasification tests. CM1
CM2
Ultimate analysis, % on weight basis ± SD C 33.0 ± 3.1 30.7 ± 1.3 H 4.4 ± 0.5 4.2 ± 0.3 N 5.6 ± 0.1 3.2 ± 0.2 S 0.3 ± 0.1 0.2 ± 0.1 Cl 0.5 ± 0.1 0.4 ± 0.1 O (by difference) 29.1 ± 2.9 25.2 ± 2.0 Moisture 9.9 ± 1.9 11.0 ± 0.6 Ashes 17.2 ± 0.4 25.1 ± 2.1 C/N ratio 5.9 9.6 Heating value (kJ kgwaste−1ar) HHV 14 590 13 670 LHV 11 940 10 980 Chemical composition of inorganic fraction (mg kgdb−1) Aluminium 210.9 344.6 Antimony 0.10 0.04 Arsenic 0.12 0.18 Cadmium 0.54 0.23 Calcium 57 930 93 200 Chromium 7.23 9.09 Cobalt 1.38 1.39 Copper 37.32 33.51 Iron 418.1 435.6 Lead 0.13 0.19 Magnesium 2936 3032 Manganese 213.0 206.8 Mercury 0.23 0.13 Nickel 2.19 3.30 Phosphorus 11 490 10 400 Potassium 16 780 14 740 Sodium 3372 4350 Tin 0.07 0.05 Vanadium 2.07 2.91 Zinc 283.7 214.3 ar, as received; db, dry basis.
the decomposition of carbonate, which is not negligible as a consequence of the high concentration of calcium in both the tested manures (Giuntoli et al., 2009).
Experimental apparatus and procedure The experimental activity was carried out in the pre-pilot scale atmospheric bubbling fluidized bed gasifier (BFBG) sketched in Figure 2, which has a feeding capacity of about 3 kg h−1. The BFBG is a 102 mm inside diameter cylindrical reactor, made of AISI 316L, which is electrically heated by five shell furnaces, each capable of a maximum power of 3.5 kW. A data acquisition/ control system connected to five, type K, thermocouples located at the reactor internal walls, regulates these heating elements and allows to independently set the temperature in each of reactor sections (blast feeding, pre-heater, bed and freeboard). The air utilized as fluidizing agent and oxidizing medium was injected with a flow of 3.5 m3N h−1 at the bed bottom through a distributor
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Di Gregorio et al. plate. The latter is composed of three nozzles, having a truncate pyramidal shape that was specifically designed to ensure a homogeneous gas distribution across the bed section. The total reactor
Figure 1. Thermal analyses (TG and DTA) of the two chicken manures tested.
height, from the metal distributor plate to the reactor outlet, is about 2.5 m. The feedstock was continuously injected into the reactor by means of a mechanical screw-feeder located about 0.20 m above the top of the expanded fluidized bed. A nitrogen flow of 0.2 m3N h−1 was used to support fuel feeding and to avoid any syngas back flow. A high efficiency cyclone is located at the reactor exit to remove dust from the syngas stream and to allow measurements of entrained carbon fines. Downstream of it there are two alternative syngas conditioning lines, both consisting of a bubbler and a filter for tar, residual fly ash, acid and basic gases. The main syngas compounds (CO, H2, CH4, CO2, N2, O2, CnHm and BTX) were measured by using an Agilent Micro-GC 3000 located downstream of the tar sampling line. The syngas was further sampled in the other two points along the reactor height (0.9 and 1.8 m), collected in Tedlar bags, and then off-line analysed. Gas and solids sampling procedures were activated when the values of pressure, temperature and gas composition were tin steady- state conditions for not less than 1 h. The sampling of condensable species was continuously performed for 30 min at a syngas flow rate of about 3 dm3N min−1, by means of a system consisting of four in-series cooling coils, a suction pump, and a flow meter. The condensed hydrocarbons were off-line analysed by means of a specific pre-treatment in a Perkin-Elmer Clarus
Figure 2. Sketch of the pre-pilot scale bubbling fluidized bed reactor.
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Results and discussion Effect of operating conditions A first series of five experimental tests were carried out with the chicken manure CM1, by keeping the fluidized bed velocity fixed (at 0.4 m s−1) and the bed material (a quartz sand having a SiO2 content of 96% and a size range of 0.2–0.4 mm), so obtaining values of reactor bed temperature between 750 and 800 °C (Arena et al., 2012). The attention was mainly focused on evaluating the influence of the equivalence ratio (ER) in terms of the main process performance parameters. As expected on the basis of previous experience with biomass wastes (Arena and Di Gregorio, 2014; Arena et al., 2010; Devi et al., 2003; Gómez-Barea et al., 2013), an increasing of equivalence ratio (from 0.27 and 0.40) determines a reduction of concentrations of carbon monoxide, hydrogen, methane and CnHm hydrocarbons (with n = 2–4), as a consequence of the larger amount of oxygen available for reaction with volatiles in the pyrolysis zone (Figure 3). The expected increase of carbon dioxide concentration is rather limited, due to the opposite effect of the Boudouard reaction (C + CO2 ↔ 2CO). The same figure shows a reduction of the total carbon losses, which indicates a lower generation of tar and carbonaceous dust, and a consequent increase (from 0.87 to 0.98) of the carbon conversion efficiency. The data related to the tests carried out at ER = 0.34 also indicate that a higher temperature could promote an increase of carbon loss, i.e. a larger production of tar and fines, and thereby a remarkable reduction of H2 and CO contents in the syngas.
Syngas composion (%v)
20%
CO, 750°C
18%
CO, 800 °C
16%
H2, 750 °C
14%
H2, 800 °C
12%
CH4, 750 °C
10%
CH4, 800 °C
8%
CiHm, 750 °C
6%
CiHm, 800 °C
4%
CO 2, 750 °C
2%
CO 2, 800 °C
0% 0.25
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Equivalence rao 45 40
Carbon loss (gc h−1)
500 gas chromatograph coupled with a mass spectrometer (GCMS). This procedure allows the identification of tar belonging to the classes between 2 and 5 of the classification system proposed by ECN (Van Paasen and Kiel, 2004). HCl, H2S and NH3 were collected by bubbling the syngas through a pair of gas strippers, connected in series (and containing basic and acid solutions, respectively), and subsequently analysed by means of a Dionex DX-120 ion chromatograph. Finally, the flow rate of syngas was determined by the ‘tie-component method’ (Felder and Rousseau, 2000) applied to the value of nitrogen content in the dry syngas, as obtained by (on-line and off-line) GC measurements, and adequately corrected to take into account the nitrogen fed into the gasifier with the waste and that leaving it as ammonia. Data collected from on-line and off-line gas measurements and from chemical analyses of solid samples were processed for each gasification test, by means of conventional mass and energy balances as well as material and substance flow analyses (MFA/SFA). MFA is a systematic assessment of the flows and stocks of materials and elements within a system defined in space and time, which is named SFA when it is referred to a specific chemical element (Brunner and Rechberger, 2004). MFA/SFA is today largely utilized to connect the sources, pathways, intermediate and final sinks of each species in a specific waste treatment process or management system, since it supplies data that are often relevant for the design, operation, and control (Arena and Di Gregorio, 2013; 2014).
T=750 °C
35
T=800 °C
30 25 20 15 10 5 0 0.25
0.30
0.35
0.40
0.45
0.50
Equivalence rao
Figure 3. Concentration of the main syngas compounds and carbon loss in the CM1 gasification tests.
The four diagrams of Figure 4 reports the variation of main process performance parameters (Arena, 2012) as a function of ER: the specific yield of syngas; its lower heating value (LHV) (excluding the contribution of tar compounds); its specific energy (the chemical energy of the producer gas per kg of poultry waste); and the cold gas efficiency (CGE, the fraction of the chemical energy of poultry waste transferred to the syngas). An increase of ER induces a reduction of syngas heating value (from about 5.0 to 3.4 MJ m−3N) and an increase in the specific syngas yield (from 1.5 to 1.9 m3N kgwaste−1). These opposite effects only partially balance to each other, and a reduction in the syngas-specific energy from about 7.5 to about 6 MJ kgwaste−1 was detected. A corresponding variation from 0.63 to 0.49 was observed in terms of CGE: the lower extreme of this range is below the generally recognized minimum acceptable for a gasification process (Higman and van der Burgt, 2003). These negative effects cannot however be attributed only to the decreasing of equivalence ratio. A comparative analysis of results reported in Figures 3 and 4 seems to indicate that the higher temperature (800 °C) at which was carried out one of the tests at ER = 0.34 leads to a worsening of the performance parameters, mainly as a consequence of the increased carbon losses. This aspect was further investigated by developing a specific material and substance flow analysis for these two tests. In particular, Figure 5 shows the layers of the feedstock energy (expressed as MJ h−1) related to the tests carried out at 750 °C (Figure 5(a)) and 800 °C (Figure 5(b)), respectively. The feedstock energy losses appear mainly concentrated inside the fluidized bed reactor, indicating the energy necessary to convert the poultry waste in a gaseous fuel. The loss of
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2.5
6.0
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5.0
Syngas LHV (MJ m-3N)
Syngas specificity yield (m3N kgwaste−1)
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CGE, -
Specific energy (MJ kgwaste−1)
Equivalence rao
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4.0
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Equivalence rao
0.35
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0.45
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Equivalence rao
Figure 4. Main process performance parameters in the CM1 gasification tests.
Figure 5. Layers of feedstock energy (MJ h−1). Tests carried out with the CM1 at ER = 0.34 for a bed temperature of 750 °C (a) and 800 °C (b). ‘I’ indicates import flow, ‘E’ indicates export flow.
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feedstock energy was equal to 12 MJ h−1, i.e. 4.1 MJ kgwaste−1 in the test at lower temperature, and to 16 MJ h−1, i.e. 5.7 MJ kgwaste−1 in that at 800 °C. As both the tests were carried out with the same waste, at the same ER, and keeping fixed all the other operating parameters, the difference should be attributed to the softening or to the partial melting of manure ash that occurs at temperatures higher than 750 °C.
Effect of ash content and composition A further series of tests was carried out with the second batch of poultry waste, CM2, received from the same farm but in a different period of time. This batch shows a thermal behaviour similar Table 2. Main operating parameters and experimental results of gasification tests with CM2. Test
A
Operating parameters Tbed (°C) 700 ER, 0.34 1.32 A/F (kgair kgwaste−1) Syngas composition 19.61 CO2 (%) CO (%) 5.05 4.61 H2 (%) 2.18 CH4 (%) 1.10 CnHm (%) BTX (%) 0.13 68 Dust (g m−3N) 11.2 Tar (g m−3N) 19 HCl (mg m−3N 0.5 H2S (mg m−3N) 904 NH3 (mg m−3N) Process performances 4.77 Syngas flow rate (m3N h−1) Syngas LHV (kJ 2800 m−3N) Specific energy 4.00 (MJ kgwaste−1) CGE 0.36
B
C
D
760 0.34 1.29
770 0.32 1.23
760 0.40 1.53
20.67 4.76 4.68 2.02 0.90 0.14 240 1.09 284 16 1897
20.33 6.86 7.17 2.20 1.15 0.16 96 1.92 74 8 5595
21.56 4.95 5.29 2.24 1.03 0.14 65 0.88 128 13 2336
4.57
4.64
4.45
2600
3400
2800
3.64
4.86
4.82
0.33
0.44
0.44
to that of CM1 (Figure 1) but a higher content of ash (25.1% instead of 17.2%), with higher fractions of calcium, phosphorous and potassium, as reported in Table 1. The first test (indicated as A in Table 2) was carried out by keeping the equivalence ratio fixed at 0.34 and reducing the reactor temperature down to 700 °C, i.e. at a value enough low to avoid possible melting or softening phenomena (Figure 1). The results indicate a dramatic reduction of all the process parameters: CGE reduces to 0.36 and the specific energy becomes as low as 4.0 MJ kgwaste−1. As this remarkable worsening of the process performance could be attributed to a much too low bed temperature, a new test (indicated as B) was carried out at the same ER but at a bed temperature of 760 °C, by using the same air preheating temperature utilized for all the tests with CM1. The results showed again a poor process performance, which definitely has to be related to the worst quality of the chicken manure CM2, mainly to its reduced LHV and higher ash content (see Table 1). This batch of chicken manure also induced a remarkable increase of calcium, phosphorous and potassium fed into the fluidized bed reactor, at about 24, 30 and 28%, respectively (Table 1). Some recent studies highlight the critical role that these alkali species can play during thermal conversion of biomass in a fluidized bed reactor (Gatternig et al., 2011; Giuntoli et al.; 2009; Yrjas et al., 2012). In particular, all these chemical elements appear to be responsible of undesired phenomena, such as the coating formation and consequent sintering and bridging between bed particles (Font-Palma, 2012). This in turn could imply agglomeration and deposit formation phenomena and, in some cases, worsening of the fluidization quality until to a definitive defluidization. In other words, it is likely that CM2 induces a larger occurrence and/or extension of these phenomena, as it is indirectly supported by the balance of feedstock energy, reported in Figure 6 for test B. The energy necessary to convert the CM2 waste in a gaseous fuel inside the reactor results to be more than 22 MJ h−1 (i.e. about 6.8 MJ kgwaste−1), then 66% larger than the value measured for the test with CM1, carried out by keeping fixed all the other operating parameters (Figure 5(a)). This larger energy consumption for the CM2
Figure 6. Layer of feedstock energy (MJ h−1). Test carried out with the CM2 at ER = 0.34 and a bed temperature of 750 °C. ‘I’ indicates import flow; ‘E’ indicates export flow.
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gasifier’ configuration, where the hot syngas is directly sent to an adequate burner, with the advantage of a potentially complete exploitation of the tar energy content (Arena, 2013). This thermal configuration has the further advantage of avoiding the necessity of a complex and often expensive syngas cleaning section (Anis and Zainal, 2011) and allows a simple Rankine cycle energy generation device to be adopted (Arena and Di Gregorio, 2014; Dunnu et al., 2012).
Conclusions
Figure 7. Thermal analyses (TG and DTA) of the ash of the two chicken manures tested.
gasification is confirmed by the thermogravimetric analyses specifically carried out on the ashes of the two chicken manures. The DTA peaks obtained in a nitrogen atmosphere and at a heating rate of 20 °C min−1 reported in Figure 7 indicate a strong difference in the thermal behaviour. The ash of CM2 shows two endothermic peaks related to phase changes in the intervals 390–490 °C and 640–850 °C, respectively. TG curves quantify the related differences in mass losses, which were 3.6 mg for CM2 and only 0.3 mg for CM1. These results and observations are in accordance with those reviewed by Font-Palma (2012), which indicated that poultry litter composition can vary significantly depending on the litter origin but also on the manure management inside the farm. In particular, the presence of potassium inside ashes has been recognized to be dependent on the type of bedding material used. An experimental investigation performed with a bubbling fluidized bed reactor detected a similar effect and identified the existence of a threshold value for the content of potassium compounds (Yrjas et al., 2012). The observations above suggest that a preliminary and careful characterization of waste properties (heating value, moisture content, ash content and composition) is absolutely necessary in order to avoid operating troubles and to optimize the conversion of the feedstock energy. In particular, the possible nonhomogeneity of the manure properties could be related to the handling and collection procedures adopted inside the farm battery limits, which have to be optimized to avoid too large amounts of floor dirt in the waste. It is likely that the utilization of chicken manure in fluidized bed gasifiers could be easier and safer by adopting a co-gasification operating mode. For instance, the co-gasification with woody biomass residues should reduce the risk of poor performance and/or bed agglomeration and, at the same time, increase the heating value of the syngas. Moreover, the heating value of the syngas could become more appealing by developing the whole process in a ‘thermal
The effects of ash composition on the gasification behaviour of two batches of chicken manure were investigated by operating a pre-pilot scale bubbling fluidized bed air-blown gasifier under different conditions of equivalence ratio and bed temperature. The contents of hydrogen, carbon monoxide and methane in the syngas as well as those of carbon losses, evaluated by taking into account elutriated fines and tar, decrease as the equivalence ratio increases. Keeping the values of equivalence ratio (at 0.34) and bed temperature (at 750 °C) fixed, the second batch of chicken manure showed a different gasification behavior, with a strong reduction of all the process performance parameters. This has been put in relation with the poorer quality of this batch, which was characterized by a reduced LHV and a higher ash content. In particular, carbon monoxide and hydrogen concentrations in the syngas halved, the cold gas efficiency dramatically reduced to 0.33 and the specific energy decreased down to 3.6 MJ kgwaste–1. A specific material flow analysis quantified the larger energy consumption inside the reactor (+66%) that was necessary to convert this second batch of poultry waste in a gaseous fuel. The thermogravimetric analyses carried out on the ashes of the two tested chicken manures assessed a strong difference in their thermal behaviour, which it is likely related to the higher fraction of alkali metals that leads to coating formation and then to sintering and bridging between bed particles. The reported experimental results indicate that the airgasification process of chicken manure in a fluidized bed is technically feasible, but a preliminary characterization of manure properties as well as an optimization of the handling and collection procedures inside the farm battery limits is necessary to avoid operating troubles and to optimize the process performances. It appears useful to adopt a ‘thermal gasifier’ configuration, where the hot syngas is directly sent to a specifically designed gas burner coupled with a Rankine cycle energy conversion device, so avoiding the necessity of a complex syngas cleaning unit and obtaining an almost complete recovery of tar heating content.
Acknowledgements The authors would like to thank Dr. Lucio Zaccariello for his assistance in part of the experimental activity.
Declaration of conflicting interests The author declares that there is no conflict of interest.
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Funding This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
References Anis S and Zainal ZA (2011) Tar reduction in biomass producer gas via mechanical, catalytic and thermal methods: A review. Renewable and Sustainable Energy Reviews 15: 2355–2377. Arena U (2012) Process and technological aspects of municipal solid waste gasification. A review. Waste Management 32: 625–639. Arena U (2013) Fluidized bed gasification. In: Scala F (ed.) Fluidized-bed Technologies for Near-zero Emission Combustion and Gasification. Cambridge, UK: Woodhead Publishing, ch. 17, pp. 765–812. Arena U and Di Gregorio F (2013) Element partinioning in combustionand gasification-based waste-to-energy units. Waste Management 33: 1142–1150. Arena U and Di Gregorio F (2014) Gasification of a solid recovered fuel in a pilot scale fluidized bed reactor. Fuel 117: 528–536. Arena U, Di Gregorio F and Santonastasi M (2010) A techno-economic comparison between two design configurations for a small scale, biomass-to-energy gasification based system. Chemical Engineering Journal 162: 580–590. Arena U, Di Gregorio F and Zaccariello L (2012) Fluidized bed gasification of a chicken manure. In Proceedings of 21st International Conference on Fluidized Bed Combustion, EnzoAlbano Editore (IT), Napoli, 3–6 June, 2012, vol. 2, pp. 752–759.. Basu P (2010) Biomass Gasification and Pyrolysis. Burlington, MA, USA: Academic Press. Boesch DF, Brinsfield RB and Magnien RE (2001) Chesapeake Bay eutrophication: scientific understanding, ecosystem restoration and challenges for agriculture. Journal of Enviromental Quality 30: 303–320. Brunner PH and Rechberger H (2004) Practical Handbook of Material Flow Analysis. Boca Raton, FL, USA: CRC Press, LLC. Cantrell KB, Ducey T, Ro KS, et al. (2008) Livestock waste-to-bioenergy generation opportunties. Bioresource Technology 99: 7941–7953. Dagnall S, Hill J and Pegg D (2000) Resource mapping and analysis of farm livestock manures-assessing the opportunities for biomass-to-energy schemes. Bioresource Technology 71: 225–234. Davalos JZ, Roux MV and Jimenez P (2002) Evaluation of poultry litter as a feasible fuel. Thermochimica Acta 394: 261–266. Devi L, Ptasinski KJ and Janssen FJJG (2003) A review of the primary measures for tar elimination in biomass gasification processes. Biomass and Bioenergy 24: 125–140. Dunnu G, Panopoulos KD, Karellas S, et al. (2012) The solid recovered fuel Stabilat: Characteristics and fluidised bed gasification tests. Fuel 93: 273–283. Felder RM and Rousseau RW (2000) Elementary Principles of Chemical Processes. New York: Wiley & Sons.
Florin NH, Maddocks AR, Wood S, et al. (2009) High-temperature thermal destruction of poultry derived wastes for energy recovery in Australia. Waste Management 29: 1399–1408. Font-Palma C (2012) Characterisation, kinetics and modelling of gasification of poultry manure and litter: An overview. Energy Conversion and Management 53: 92–98.. Gatternig B, Hohenwarter U, Schröttner H, et al. (2011) The influence of volatile alkali species on coating formation in biomass fired fluidize beds. 18th Biomass Conference and Exhibition, Lyon, France. Giuntoli J, De Jong W, Arvelakis S, et al. (2009) Quantitative and kinetic TG-FTIR study of biomass residue pyrolysis: Dry distiller’s grains with solubles (DDGS) and chicken manure. Journal of Analytical and Applied Pyrolysis 85: 301–312. Gómez-Barea A, Ollero P and Leckner B (2013) Optimization of char and tar conversion in fluidized bed biomass gasifiers. Fuel 103: 42–52. Heathman GC, Sharpley AN, Smith SJ, et al. (1995) Land application of poultry litter and water quality in Oklahoma U.S.A. Fertilizer Research 40: 165–173. Higman C and van der Burgt M (2003) Gasification. Burlington, MA, USA: Gulf Professional Publishing. Jackson BP, Seaman JC and Bertsch PM (2006) Fate of arsenic compounds in poultry litter upon land application. Chemosphere 65: 2028–2034. Otero M, Sanchez ME and Gomez X (2011) Co-firing of coal and manure biomass: A TG-MS approach. Bioresource Technology 102: 8304– 8309. Quiroga G, Castrillon L, Fernandez-Nava Y, et al. (2010) Physicochemical analysis and calorific values of poultry manure. Waste Management 30: 880–884. Sheng C and Azevedo JLT (2005) Estimating the higher heating value of biomass fuels from basic analysis data. Biomass Bioenergy 28: 499–507. UNA – Unione Nazionale dell’Avicoltura (2010) Available on http:/www. unionenazionaleavicoltura.it/pdf/varie/commenti2010.pdf (accessed 29 January 2013). Van Paasen SVB and Kiel JHA (2004) Tar formation in fluidised-bed gasification-impact of gasifier operating conditions. In: Proceedings of 2nd World Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection, Rome, Italy. Yrjas P, Sevonius C and Hupa M (2012) Bed agglomeration due to addition of KCl and K2CO3 – first results from a laboratory fluidized bed reactor. In: Proceedings of 21st International Conference on Fluidized Bed Combustion, EnzoAlbano Editore (IT), Napoli, 3–6 June, 2012, vol. 1, pp. 203–210. Zhang SY, Cao JP and Takarada T (2009) Effect of pretreatment with different washing methods on the reactivity of manure char. Bioresource Technology 101: 6130–6135. Zhu S and Lee SW (2005) Co-combustion of poultry wastes and natural gas in the advanced swirling fluidized bed combustor (SFBC). Waste Management 25: 511–518.
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The effect of ash composition on gasification of poultry wastes in a fluidized bed reactor Fabrizio Di Gregorio, Donato Santoro and Umberto Arena Waste Manag Res 2014 32: 323 originally published online 17 March 2014 DOI: 10.1177/0734242X14525821 The online version of this article can be found at: http://wmr.sagepub.com/content/32/4/323
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WMR0010.1177/0734242X14525821Waste Management & ResearchDi Gregorio et al.
Original Article
The effect of ash composition on gasification of poultry wastes in a fluidized bed reactor
Waste Management & Research 2014, Vol. 32(4) 323–330 © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0734242X14525821 wmr.sagepub.com
Fabrizio Di Gregorio1, Donato Santoro2 and Umberto Arena2
Abstract The effect of ash composition on the fluidized bed gasification behaviour of poultry wastes was investigated by operating a prepilot scale reactor with two batches of manure obtained from an industrial chicken farm. The experimental runs were carried out by keeping the fluidized bed velocity fixed (at 0.4m s−1) and by varying the equivalence ratio between 0.27 and 0.40, so obtaining bed temperature values between 700 and 800 °C. The performance of the gasification process was assessed by means of mass balances as well as material and feedstock energy analyses, and reported in terms of cold gas efficiency (CGE), specific energy production, low heating value of obtained syngas and yield of undesired by-products. The experimental results indicate the crucial role of ash amount and composition of the two poultry wastes. In particular, higher ash content (25.1% instead of 17.2%) and higher fractions of calcium, phosphorous and potassium (with an increase of 24, 30 and 28%, respectively) induce a dramatic reduction of all the process performance parameters: CGE reduces from 0.63 to 0.33 and the specific energy from 2.1 to 1.1 kWh kgfuel−1. At the same time, the formation of alkali compounds and their behaviour inside the fluidized bed reactor determine an increase of feedstock energy losses, which is related to occurrence of sintering and bridging between bed particles. Keywords Chicken manure, poultry waste, gasification, bubbling fluidized bed, sintering, feedstock energy: wmr 13-0233
Introduction The intensive increase in the worldwide population implies an exponential growth in the demand for food. This aspect, together with the low production cost of poultry meat has led to a growing number of intensive farms and to a rapid expansion of the global market. For instance, the Italian poultry industry, which is one of the Europe’s largest producer and exporter of poultry meat (covering about 12% of the overall market), generates a turnover of €5300 million, mainly related to the national consumption (UNA, 2010). At the same time, the proliferation of chicken farms produces millions of tons of manure by-products which, until the beginning of 2000, were conventionally sent to landfill. The necessity for an adequate treatment of pathogen agents and heavy metals (Jackson et al., 2006) and for avoiding potential eutrophication effects (Heathman et al., 1995) has led to stringent environmental legislations (Boesch et al., 2001; Dagnall et al., 2000) and to the requirement of alternative management options. The bio-chemical (composting and anaerobic digestion) and thermo-chemical (combustion and gasification) conversion processes, as well as their possible combinations, have been recently assessed as potentially sustainable management solutions (Cantrell et al., 2008). The bio-chemical units allow mass and volume reduction together with the destruction of pathogens but they need
additional equipment and handling costs and appear not suitable to solve the aspects related to nutrient losses and heavy metal contamination (Florin et al., 2009). The thermo-chemical units appear to be more convenient from the economic and environmental points of view, owing to their capability to destroy pathogen agents, to remarkably reduce the mass of waste, and to provide a certain amount of energy (Zhu and Lee, 2005). In particular, gasification may be used to convert the poultry farm waste into a fuel gas (‘syngas’), which can be efficiently burned in a dedicated energy conversion device (Zhang et al., 2009). On the other hand, problems associated with the formation and release of different contaminants (tar, ashes, heavy metals, 1AMRA
s.c. a r.l. – Analysis and Monitoring of Environmental Risk, Via Nuova Agnano, Naples, Italy 2Department of Environmental, Biological and Pharmaceutical Sciences and Technologies – Second University of Naples, Caserta, Italy Corresponding author: Umberto Arena, Department of Environmental, Biological and Pharmaceutical Sciences and Technologies – Second University of Naples, Via A.Vivaldi, 43, Caserta, 81100, Italy. Email: [email protected]
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halogens and alkaline compounds) could cause environmental and operating problems, such as wastewater pollution; material corrosion; clogging or blockage in fuel lines, filters, heat exchangers and energy conversion devices (Arena, 2012). These aspects still represent some crucial obstacles to be overcome. The study aims to evaluate the performances of an air gasification process of chicken manure, carried out in a bubbling fluidized bed reactor operated under different values of equivalence ratio (defined as the oxygen content of air supply with respect to that required for the stoichiometric complete combustion of the fuel effectively fed to the reactor). Fluidization is the most promising among all biomass gasification technologies, due to its peculiar characteristics and, in particular, the possibility of utilizing different fluidizing agents, reactor temperatures and gas residence times, to inject reagents at different reactor heights and to operate with or without a specific catalyst (Arena, 2013; Basu, 2010). An appropriate utilization of these features could thus be the key to an efficient and sustainable management of this kind of waste.
Material and methods Characterization of chicken manure tested Two batches of chicken manure derived by an Italian poultry farm, as collected in two different seasons, were used as feedstock. The wastes, identified in the following as CM1 and CM2, were both obtained by the same random sampling method in the chicken farm storage area. Their ultimate analysis was obtained by means of a Leco Truspec CHNS analyser, while the composition of the inorganic fraction was determined by an Agilent 7500 ICP-MS. Table 1 reports these analyses together with the moisture and ash contents, and the heating values evaluated by means of the relationship proposed by Sheng and Azevedo (2005). It is worth noting that the data in Table 1 are very close to those reported by the main scientific literature in the field (Davalos et al., 2002; Font-Palma, 2012; Giuntoli et al., 2009; Quiroga et al., 2010). Figure 1 shows the thermal analyses of the two wastes, as obtained by a Perkin-Elmer Pyris Diamond thermogravimetric differential thermal analyser (TG/DTA), operated with nitrogen and at a heating rate of 20 °C min−1. The curves of TG (sample weight losses) and DTA (endo- or exo-thermic nature of the reactions) seem to predict a sufficiently similar behaviour of the two wastes, with most of the material decomposed between 280 and 710 °C. This range is quite similar to those found by Giuntoli et al. (2009), who analysed an untreated and a leached chicken manure and by Otero et al. (2011), who analysed a manure characterized by a very similar ultimate analysis. It is likely that the first peaks along the DTA curve (i.e. those around 280 and 320 °C) represent the decomposition of non-digested food, which occurs with the release of ammonia contained in the manure (Font-Palma, 2012). The other peaks are probably due to the decomposition of the manure, with the release of methane at about 530 °C. The last peak (at about 770 °C) could be related to
Table 1. Main chemical properties of the chicken manure utilized for the gasification tests. CM1
CM2
Ultimate analysis, % on weight basis ± SD C 33.0 ± 3.1 30.7 ± 1.3 H 4.4 ± 0.5 4.2 ± 0.3 N 5.6 ± 0.1 3.2 ± 0.2 S 0.3 ± 0.1 0.2 ± 0.1 Cl 0.5 ± 0.1 0.4 ± 0.1 O (by difference) 29.1 ± 2.9 25.2 ± 2.0 Moisture 9.9 ± 1.9 11.0 ± 0.6 Ashes 17.2 ± 0.4 25.1 ± 2.1 C/N ratio 5.9 9.6 Heating value (kJ kgwaste−1ar) HHV 14 590 13 670 LHV 11 940 10 980 Chemical composition of inorganic fraction (mg kgdb−1) Aluminium 210.9 344.6 Antimony 0.10 0.04 Arsenic 0.12 0.18 Cadmium 0.54 0.23 Calcium 57 930 93 200 Chromium 7.23 9.09 Cobalt 1.38 1.39 Copper 37.32 33.51 Iron 418.1 435.6 Lead 0.13 0.19 Magnesium 2936 3032 Manganese 213.0 206.8 Mercury 0.23 0.13 Nickel 2.19 3.30 Phosphorus 11 490 10 400 Potassium 16 780 14 740 Sodium 3372 4350 Tin 0.07 0.05 Vanadium 2.07 2.91 Zinc 283.7 214.3 ar, as received; db, dry basis.
the decomposition of carbonate, which is not negligible as a consequence of the high concentration of calcium in both the tested manures (Giuntoli et al., 2009).
Experimental apparatus and procedure The experimental activity was carried out in the pre-pilot scale atmospheric bubbling fluidized bed gasifier (BFBG) sketched in Figure 2, which has a feeding capacity of about 3 kg h−1. The BFBG is a 102 mm inside diameter cylindrical reactor, made of AISI 316L, which is electrically heated by five shell furnaces, each capable of a maximum power of 3.5 kW. A data acquisition/ control system connected to five, type K, thermocouples located at the reactor internal walls, regulates these heating elements and allows to independently set the temperature in each of reactor sections (blast feeding, pre-heater, bed and freeboard). The air utilized as fluidizing agent and oxidizing medium was injected with a flow of 3.5 m3N h−1 at the bed bottom through a distributor
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Di Gregorio et al. plate. The latter is composed of three nozzles, having a truncate pyramidal shape that was specifically designed to ensure a homogeneous gas distribution across the bed section. The total reactor
Figure 1. Thermal analyses (TG and DTA) of the two chicken manures tested.
height, from the metal distributor plate to the reactor outlet, is about 2.5 m. The feedstock was continuously injected into the reactor by means of a mechanical screw-feeder located about 0.20 m above the top of the expanded fluidized bed. A nitrogen flow of 0.2 m3N h−1 was used to support fuel feeding and to avoid any syngas back flow. A high efficiency cyclone is located at the reactor exit to remove dust from the syngas stream and to allow measurements of entrained carbon fines. Downstream of it there are two alternative syngas conditioning lines, both consisting of a bubbler and a filter for tar, residual fly ash, acid and basic gases. The main syngas compounds (CO, H2, CH4, CO2, N2, O2, CnHm and BTX) were measured by using an Agilent Micro-GC 3000 located downstream of the tar sampling line. The syngas was further sampled in the other two points along the reactor height (0.9 and 1.8 m), collected in Tedlar bags, and then off-line analysed. Gas and solids sampling procedures were activated when the values of pressure, temperature and gas composition were tin steady- state conditions for not less than 1 h. The sampling of condensable species was continuously performed for 30 min at a syngas flow rate of about 3 dm3N min−1, by means of a system consisting of four in-series cooling coils, a suction pump, and a flow meter. The condensed hydrocarbons were off-line analysed by means of a specific pre-treatment in a Perkin-Elmer Clarus
Figure 2. Sketch of the pre-pilot scale bubbling fluidized bed reactor.
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Results and discussion Effect of operating conditions A first series of five experimental tests were carried out with the chicken manure CM1, by keeping the fluidized bed velocity fixed (at 0.4 m s−1) and the bed material (a quartz sand having a SiO2 content of 96% and a size range of 0.2–0.4 mm), so obtaining values of reactor bed temperature between 750 and 800 °C (Arena et al., 2012). The attention was mainly focused on evaluating the influence of the equivalence ratio (ER) in terms of the main process performance parameters. As expected on the basis of previous experience with biomass wastes (Arena and Di Gregorio, 2014; Arena et al., 2010; Devi et al., 2003; Gómez-Barea et al., 2013), an increasing of equivalence ratio (from 0.27 and 0.40) determines a reduction of concentrations of carbon monoxide, hydrogen, methane and CnHm hydrocarbons (with n = 2–4), as a consequence of the larger amount of oxygen available for reaction with volatiles in the pyrolysis zone (Figure 3). The expected increase of carbon dioxide concentration is rather limited, due to the opposite effect of the Boudouard reaction (C + CO2 ↔ 2CO). The same figure shows a reduction of the total carbon losses, which indicates a lower generation of tar and carbonaceous dust, and a consequent increase (from 0.87 to 0.98) of the carbon conversion efficiency. The data related to the tests carried out at ER = 0.34 also indicate that a higher temperature could promote an increase of carbon loss, i.e. a larger production of tar and fines, and thereby a remarkable reduction of H2 and CO contents in the syngas.
Syngas composion (%v)
20%
CO, 750°C
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H2, 750 °C
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H2, 800 °C
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CH4, 750 °C
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500 gas chromatograph coupled with a mass spectrometer (GCMS). This procedure allows the identification of tar belonging to the classes between 2 and 5 of the classification system proposed by ECN (Van Paasen and Kiel, 2004). HCl, H2S and NH3 were collected by bubbling the syngas through a pair of gas strippers, connected in series (and containing basic and acid solutions, respectively), and subsequently analysed by means of a Dionex DX-120 ion chromatograph. Finally, the flow rate of syngas was determined by the ‘tie-component method’ (Felder and Rousseau, 2000) applied to the value of nitrogen content in the dry syngas, as obtained by (on-line and off-line) GC measurements, and adequately corrected to take into account the nitrogen fed into the gasifier with the waste and that leaving it as ammonia. Data collected from on-line and off-line gas measurements and from chemical analyses of solid samples were processed for each gasification test, by means of conventional mass and energy balances as well as material and substance flow analyses (MFA/SFA). MFA is a systematic assessment of the flows and stocks of materials and elements within a system defined in space and time, which is named SFA when it is referred to a specific chemical element (Brunner and Rechberger, 2004). MFA/SFA is today largely utilized to connect the sources, pathways, intermediate and final sinks of each species in a specific waste treatment process or management system, since it supplies data that are often relevant for the design, operation, and control (Arena and Di Gregorio, 2013; 2014).
T=750 °C
35
T=800 °C
30 25 20 15 10 5 0 0.25
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Equivalence rao
Figure 3. Concentration of the main syngas compounds and carbon loss in the CM1 gasification tests.
The four diagrams of Figure 4 reports the variation of main process performance parameters (Arena, 2012) as a function of ER: the specific yield of syngas; its lower heating value (LHV) (excluding the contribution of tar compounds); its specific energy (the chemical energy of the producer gas per kg of poultry waste); and the cold gas efficiency (CGE, the fraction of the chemical energy of poultry waste transferred to the syngas). An increase of ER induces a reduction of syngas heating value (from about 5.0 to 3.4 MJ m−3N) and an increase in the specific syngas yield (from 1.5 to 1.9 m3N kgwaste−1). These opposite effects only partially balance to each other, and a reduction in the syngas-specific energy from about 7.5 to about 6 MJ kgwaste−1 was detected. A corresponding variation from 0.63 to 0.49 was observed in terms of CGE: the lower extreme of this range is below the generally recognized minimum acceptable for a gasification process (Higman and van der Burgt, 2003). These negative effects cannot however be attributed only to the decreasing of equivalence ratio. A comparative analysis of results reported in Figures 3 and 4 seems to indicate that the higher temperature (800 °C) at which was carried out one of the tests at ER = 0.34 leads to a worsening of the performance parameters, mainly as a consequence of the increased carbon losses. This aspect was further investigated by developing a specific material and substance flow analysis for these two tests. In particular, Figure 5 shows the layers of the feedstock energy (expressed as MJ h−1) related to the tests carried out at 750 °C (Figure 5(a)) and 800 °C (Figure 5(b)), respectively. The feedstock energy losses appear mainly concentrated inside the fluidized bed reactor, indicating the energy necessary to convert the poultry waste in a gaseous fuel. The loss of
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Figure 4. Main process performance parameters in the CM1 gasification tests.
Figure 5. Layers of feedstock energy (MJ h−1). Tests carried out with the CM1 at ER = 0.34 for a bed temperature of 750 °C (a) and 800 °C (b). ‘I’ indicates import flow, ‘E’ indicates export flow.
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feedstock energy was equal to 12 MJ h−1, i.e. 4.1 MJ kgwaste−1 in the test at lower temperature, and to 16 MJ h−1, i.e. 5.7 MJ kgwaste−1 in that at 800 °C. As both the tests were carried out with the same waste, at the same ER, and keeping fixed all the other operating parameters, the difference should be attributed to the softening or to the partial melting of manure ash that occurs at temperatures higher than 750 °C.
Effect of ash content and composition A further series of tests was carried out with the second batch of poultry waste, CM2, received from the same farm but in a different period of time. This batch shows a thermal behaviour similar Table 2. Main operating parameters and experimental results of gasification tests with CM2. Test
A
Operating parameters Tbed (°C) 700 ER, 0.34 1.32 A/F (kgair kgwaste−1) Syngas composition 19.61 CO2 (%) CO (%) 5.05 4.61 H2 (%) 2.18 CH4 (%) 1.10 CnHm (%) BTX (%) 0.13 68 Dust (g m−3N) 11.2 Tar (g m−3N) 19 HCl (mg m−3N 0.5 H2S (mg m−3N) 904 NH3 (mg m−3N) Process performances 4.77 Syngas flow rate (m3N h−1) Syngas LHV (kJ 2800 m−3N) Specific energy 4.00 (MJ kgwaste−1) CGE 0.36
B
C
D
760 0.34 1.29
770 0.32 1.23
760 0.40 1.53
20.67 4.76 4.68 2.02 0.90 0.14 240 1.09 284 16 1897
20.33 6.86 7.17 2.20 1.15 0.16 96 1.92 74 8 5595
21.56 4.95 5.29 2.24 1.03 0.14 65 0.88 128 13 2336
4.57
4.64
4.45
2600
3400
2800
3.64
4.86
4.82
0.33
0.44
0.44
to that of CM1 (Figure 1) but a higher content of ash (25.1% instead of 17.2%), with higher fractions of calcium, phosphorous and potassium, as reported in Table 1. The first test (indicated as A in Table 2) was carried out by keeping the equivalence ratio fixed at 0.34 and reducing the reactor temperature down to 700 °C, i.e. at a value enough low to avoid possible melting or softening phenomena (Figure 1). The results indicate a dramatic reduction of all the process parameters: CGE reduces to 0.36 and the specific energy becomes as low as 4.0 MJ kgwaste−1. As this remarkable worsening of the process performance could be attributed to a much too low bed temperature, a new test (indicated as B) was carried out at the same ER but at a bed temperature of 760 °C, by using the same air preheating temperature utilized for all the tests with CM1. The results showed again a poor process performance, which definitely has to be related to the worst quality of the chicken manure CM2, mainly to its reduced LHV and higher ash content (see Table 1). This batch of chicken manure also induced a remarkable increase of calcium, phosphorous and potassium fed into the fluidized bed reactor, at about 24, 30 and 28%, respectively (Table 1). Some recent studies highlight the critical role that these alkali species can play during thermal conversion of biomass in a fluidized bed reactor (Gatternig et al., 2011; Giuntoli et al.; 2009; Yrjas et al., 2012). In particular, all these chemical elements appear to be responsible of undesired phenomena, such as the coating formation and consequent sintering and bridging between bed particles (Font-Palma, 2012). This in turn could imply agglomeration and deposit formation phenomena and, in some cases, worsening of the fluidization quality until to a definitive defluidization. In other words, it is likely that CM2 induces a larger occurrence and/or extension of these phenomena, as it is indirectly supported by the balance of feedstock energy, reported in Figure 6 for test B. The energy necessary to convert the CM2 waste in a gaseous fuel inside the reactor results to be more than 22 MJ h−1 (i.e. about 6.8 MJ kgwaste−1), then 66% larger than the value measured for the test with CM1, carried out by keeping fixed all the other operating parameters (Figure 5(a)). This larger energy consumption for the CM2
Figure 6. Layer of feedstock energy (MJ h−1). Test carried out with the CM2 at ER = 0.34 and a bed temperature of 750 °C. ‘I’ indicates import flow; ‘E’ indicates export flow.
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gasifier’ configuration, where the hot syngas is directly sent to an adequate burner, with the advantage of a potentially complete exploitation of the tar energy content (Arena, 2013). This thermal configuration has the further advantage of avoiding the necessity of a complex and often expensive syngas cleaning section (Anis and Zainal, 2011) and allows a simple Rankine cycle energy generation device to be adopted (Arena and Di Gregorio, 2014; Dunnu et al., 2012).
Conclusions
Figure 7. Thermal analyses (TG and DTA) of the ash of the two chicken manures tested.
gasification is confirmed by the thermogravimetric analyses specifically carried out on the ashes of the two chicken manures. The DTA peaks obtained in a nitrogen atmosphere and at a heating rate of 20 °C min−1 reported in Figure 7 indicate a strong difference in the thermal behaviour. The ash of CM2 shows two endothermic peaks related to phase changes in the intervals 390–490 °C and 640–850 °C, respectively. TG curves quantify the related differences in mass losses, which were 3.6 mg for CM2 and only 0.3 mg for CM1. These results and observations are in accordance with those reviewed by Font-Palma (2012), which indicated that poultry litter composition can vary significantly depending on the litter origin but also on the manure management inside the farm. In particular, the presence of potassium inside ashes has been recognized to be dependent on the type of bedding material used. An experimental investigation performed with a bubbling fluidized bed reactor detected a similar effect and identified the existence of a threshold value for the content of potassium compounds (Yrjas et al., 2012). The observations above suggest that a preliminary and careful characterization of waste properties (heating value, moisture content, ash content and composition) is absolutely necessary in order to avoid operating troubles and to optimize the conversion of the feedstock energy. In particular, the possible nonhomogeneity of the manure properties could be related to the handling and collection procedures adopted inside the farm battery limits, which have to be optimized to avoid too large amounts of floor dirt in the waste. It is likely that the utilization of chicken manure in fluidized bed gasifiers could be easier and safer by adopting a co-gasification operating mode. For instance, the co-gasification with woody biomass residues should reduce the risk of poor performance and/or bed agglomeration and, at the same time, increase the heating value of the syngas. Moreover, the heating value of the syngas could become more appealing by developing the whole process in a ‘thermal
The effects of ash composition on the gasification behaviour of two batches of chicken manure were investigated by operating a pre-pilot scale bubbling fluidized bed air-blown gasifier under different conditions of equivalence ratio and bed temperature. The contents of hydrogen, carbon monoxide and methane in the syngas as well as those of carbon losses, evaluated by taking into account elutriated fines and tar, decrease as the equivalence ratio increases. Keeping the values of equivalence ratio (at 0.34) and bed temperature (at 750 °C) fixed, the second batch of chicken manure showed a different gasification behavior, with a strong reduction of all the process performance parameters. This has been put in relation with the poorer quality of this batch, which was characterized by a reduced LHV and a higher ash content. In particular, carbon monoxide and hydrogen concentrations in the syngas halved, the cold gas efficiency dramatically reduced to 0.33 and the specific energy decreased down to 3.6 MJ kgwaste–1. A specific material flow analysis quantified the larger energy consumption inside the reactor (+66%) that was necessary to convert this second batch of poultry waste in a gaseous fuel. The thermogravimetric analyses carried out on the ashes of the two tested chicken manures assessed a strong difference in their thermal behaviour, which it is likely related to the higher fraction of alkali metals that leads to coating formation and then to sintering and bridging between bed particles. The reported experimental results indicate that the airgasification process of chicken manure in a fluidized bed is technically feasible, but a preliminary characterization of manure properties as well as an optimization of the handling and collection procedures inside the farm battery limits is necessary to avoid operating troubles and to optimize the process performances. It appears useful to adopt a ‘thermal gasifier’ configuration, where the hot syngas is directly sent to a specifically designed gas burner coupled with a Rankine cycle energy conversion device, so avoiding the necessity of a complex syngas cleaning unit and obtaining an almost complete recovery of tar heating content.
Acknowledgements The authors would like to thank Dr. Lucio Zaccariello for his assistance in part of the experimental activity.
Declaration of conflicting interests The author declares that there is no conflict of interest.
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Funding This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
References Anis S and Zainal ZA (2011) Tar reduction in biomass producer gas via mechanical, catalytic and thermal methods: A review. Renewable and Sustainable Energy Reviews 15: 2355–2377. Arena U (2012) Process and technological aspects of municipal solid waste gasification. A review. Waste Management 32: 625–639. Arena U (2013) Fluidized bed gasification. In: Scala F (ed.) Fluidized-bed Technologies for Near-zero Emission Combustion and Gasification. Cambridge, UK: Woodhead Publishing, ch. 17, pp. 765–812. Arena U and Di Gregorio F (2013) Element partinioning in combustionand gasification-based waste-to-energy units. Waste Management 33: 1142–1150. Arena U and Di Gregorio F (2014) Gasification of a solid recovered fuel in a pilot scale fluidized bed reactor. Fuel 117: 528–536. Arena U, Di Gregorio F and Santonastasi M (2010) A techno-economic comparison between two design configurations for a small scale, biomass-to-energy gasification based system. Chemical Engineering Journal 162: 580–590. Arena U, Di Gregorio F and Zaccariello L (2012) Fluidized bed gasification of a chicken manure. In Proceedings of 21st International Conference on Fluidized Bed Combustion, EnzoAlbano Editore (IT), Napoli, 3–6 June, 2012, vol. 2, pp. 752–759.. Basu P (2010) Biomass Gasification and Pyrolysis. Burlington, MA, USA: Academic Press. Boesch DF, Brinsfield RB and Magnien RE (2001) Chesapeake Bay eutrophication: scientific understanding, ecosystem restoration and challenges for agriculture. Journal of Enviromental Quality 30: 303–320. Brunner PH and Rechberger H (2004) Practical Handbook of Material Flow Analysis. Boca Raton, FL, USA: CRC Press, LLC. Cantrell KB, Ducey T, Ro KS, et al. (2008) Livestock waste-to-bioenergy generation opportunties. Bioresource Technology 99: 7941–7953. Dagnall S, Hill J and Pegg D (2000) Resource mapping and analysis of farm livestock manures-assessing the opportunities for biomass-to-energy schemes. Bioresource Technology 71: 225–234. Davalos JZ, Roux MV and Jimenez P (2002) Evaluation of poultry litter as a feasible fuel. Thermochimica Acta 394: 261–266. Devi L, Ptasinski KJ and Janssen FJJG (2003) A review of the primary measures for tar elimination in biomass gasification processes. Biomass and Bioenergy 24: 125–140. Dunnu G, Panopoulos KD, Karellas S, et al. (2012) The solid recovered fuel Stabilat: Characteristics and fluidised bed gasification tests. Fuel 93: 273–283. Felder RM and Rousseau RW (2000) Elementary Principles of Chemical Processes. New York: Wiley & Sons.
Florin NH, Maddocks AR, Wood S, et al. (2009) High-temperature thermal destruction of poultry derived wastes for energy recovery in Australia. Waste Management 29: 1399–1408. Font-Palma C (2012) Characterisation, kinetics and modelling of gasification of poultry manure and litter: An overview. Energy Conversion and Management 53: 92–98.. Gatternig B, Hohenwarter U, Schröttner H, et al. (2011) The influence of volatile alkali species on coating formation in biomass fired fluidize beds. 18th Biomass Conference and Exhibition, Lyon, France. Giuntoli J, De Jong W, Arvelakis S, et al. (2009) Quantitative and kinetic TG-FTIR study of biomass residue pyrolysis: Dry distiller’s grains with solubles (DDGS) and chicken manure. Journal of Analytical and Applied Pyrolysis 85: 301–312. Gómez-Barea A, Ollero P and Leckner B (2013) Optimization of char and tar conversion in fluidized bed biomass gasifiers. Fuel 103: 42–52. Heathman GC, Sharpley AN, Smith SJ, et al. (1995) Land application of poultry litter and water quality in Oklahoma U.S.A. Fertilizer Research 40: 165–173. Higman C and van der Burgt M (2003) Gasification. Burlington, MA, USA: Gulf Professional Publishing. Jackson BP, Seaman JC and Bertsch PM (2006) Fate of arsenic compounds in poultry litter upon land application. Chemosphere 65: 2028–2034. Otero M, Sanchez ME and Gomez X (2011) Co-firing of coal and manure biomass: A TG-MS approach. Bioresource Technology 102: 8304– 8309. Quiroga G, Castrillon L, Fernandez-Nava Y, et al. (2010) Physicochemical analysis and calorific values of poultry manure. Waste Management 30: 880–884. Sheng C and Azevedo JLT (2005) Estimating the higher heating value of biomass fuels from basic analysis data. Biomass Bioenergy 28: 499–507. UNA – Unione Nazionale dell’Avicoltura (2010) Available on http:/www. unionenazionaleavicoltura.it/pdf/varie/commenti2010.pdf (accessed 29 January 2013). Van Paasen SVB and Kiel JHA (2004) Tar formation in fluidised-bed gasification-impact of gasifier operating conditions. In: Proceedings of 2nd World Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection, Rome, Italy. Yrjas P, Sevonius C and Hupa M (2012) Bed agglomeration due to addition of KCl and K2CO3 – first results from a laboratory fluidized bed reactor. In: Proceedings of 21st International Conference on Fluidized Bed Combustion, EnzoAlbano Editore (IT), Napoli, 3–6 June, 2012, vol. 1, pp. 203–210. Zhang SY, Cao JP and Takarada T (2009) Effect of pretreatment with different washing methods on the reactivity of manure char. Bioresource Technology 101: 6130–6135. Zhu S and Lee SW (2005) Co-combustion of poultry wastes and natural gas in the advanced swirling fluidized bed combustor (SFBC). Waste Management 25: 511–518.
Downloaded from wmr.sagepub.com at UVI - Biblioteca Central on April 23, 2014
